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g UNITED STATES PATENT O CARL MOLDENHAUER, OF FRANKFORT-ON-THE-MAIN, GERMANY.

MEIHOD F PRECIPITATING PRECIOUS METALS FROM SOLUTIONS.

SPECIFICATION forming part of Letters Patent No. 532,238, dated January 8, 1 895.

Application filed May 5, 1894; S rial No, 510,147. (No specimens.)

To all whom it may concern.-

Be it known that I, CARL MOLDENHAUER, a subject ofthe Emperor of Germany, residing at Frankfort-on-the-Main, Germany, have invented certain new and useful Improvements ,in Methods of Precipitating Gold or other Precious Metals Out of Their Acid Solutions, of which the following is a specification.

This invention has reference to an improved process of dissolving gold and other precious metals from their ores by means of acid cyanide-solutions, precipitating the gold from said solutions by means of aluminum and regenerating the cyanide-solution so as to enable it to dissolve a new quantity of precious metal out of its ores.

In the Letters Patent No. 512,046 heretofore granted to me on January 2, 1894., I have described a process of precipitating precious metals from their cyanide-solutions by means of aluminum in the presence of afree alkali.

In following up my researches, I have found that aluminum and its alloys or amalgams can be used with the'same advantage for precipitating gold or other precious metals from acid cyanide-solutions, and that the remaining solution can be regenerated by adding, after the precipitation has taken place, a free alkali or an alkaline earth.

In carrying out my improved process, the gold or other precious metal is dissolved from its ores by means of a cyanide-solution, in which a free acid, such as sulfuric acid for instance, is present in place-of a free alkali. Aluminum is then added to the solution, so that the reaction and the precipitation of gold take place in compliance with the fol- The free-cyanic acid, which is thus obtained besides alumina and potassium sulfate would not be capable of dissolving gold' out of its ores, and it is therefore necessary to add to the solution a free alkali after the precipitation of gold has taken place. alkali combines then immediately with the free cyanic acid present in the solution, so as to form a cyanide which is capable of dissolving a new quantity of gold from its ores. In other words, the cyanide-solution is regenerated, so that it can be used for the next reaction and so on. In place of a free alkali, an alkaline earth may be used with the same advantage.

Having thus described my invention, I claim as new and desire to secure by Letters Patent The process herein'described of dissolving gold and other precious metals from the ores by means of cyanide-solutions, which con sists in subjecting the ores to the action of an acid cyanide-solution so as to dissolve the gold or other precious metal, then adding aluminum so as to precipitate the gold or other metal from the solution, and regenerating the cyanide-solution by means of a free alkali or alkaline earth, substantially as set forth. 1

In testimony that I claim the foregoing as my invention I have signed my name in presence of two subscribing witnesses.

CARL MOLDENHAUER.

Witnesses:

ALvEsTo S. HOGUE, JEAN GRUND.

This- 

